A substantial amount of work has been done in the development of ceramic superconductor composite wires. As is disclosed in an article by Gil N. Riley, Jr. et. al. entitled "Commercialization of Ceramic Superconductor Composite Wires" (American Ceramic Society Bulletin, Volume 72, No. 7, July, 1993, at pages 91-97), "Recent advances in the development of high-temperature superconductor. . . composite wires demonstrate an increasingly realistic potential for commercial applications, such as power transmission cables, motors, and superconducting magnetic energy storage . . . systems."
As is disclosed in the Riley article, the most promising superconductive composite wire contains a core consisting of the bismuth-strontium-calcium-copper superconductive material and a silver sheath. This wire, however, only operates satisfactorily at temperatures below about 20 degrees Kelvin.
The well-known 1-2-3 yttrium-barium-copper superconductive phase has a phase transition temperature of about 93 degrees Kelvin; and, if it were known how to make a sheath--core fiber from it, such fiber would operate satisfactorily at a temperature above 77 degrees Kelvin.
The conventional means of producing ceramic superconductor composite wires is to charge the precursor powders of the superconductive material into a silver tube, deform the filled tube into a wire of desired diameter, and then fire the filled tube to convert the powder into the desired superconductor. See, e.g., the Master's thesis of Barton C. Prorok entitled "Formation of the Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x Superconductor by a Two Powder Process" which available from the University of Illinois at Chicago (1993).
Because of the relatively low melting point of silver, (962 degrees centigrade), and the relatively high temperature necessary to sinter the 1-2-3 phase (about 960 degrees centigrade), it has heretofore been very difficult to produce the silver/1-2-3 sheath/core wire.
Not every metal can be used as a sheath for superconductive wire. Although silver ion does not effect the activity of the 1-2-3 phase, other metals tend to destroy such activity. Thus, when nickel is substituted for silver as the sheath material and the nickel/1-2-3 precursor assembly is fired, nickel ion replaces the copper in the 1-2-3 structure and destroys its superconductivity. See, e.g., an article by H. M. Meyer et. al. entitled "Ni/YBa.sub.2 Cu.sub.3 O.sub.7-x. . . formation . . . " appearing in the Journal of Material Research, Volume 6, No. 2, February, 1991, pages 270-277.
It is an object of this invention to provide a plasma process for preparing a ceramic superconductor composite wire which will be superconductive at temperatures in excess of 77 degrees Kelvin and which, additionally, may be used for large scale, economical production of the composite wire.
It is another object of this invention to prepare an intermediate which, after firing, may be formed into a ceramic superconductor composite wire.